Currently, strong demand for energy and uncertain supplies have created interest in tapping unconventional reservoirs. Reservoirs with low permeability are difficult to recover using conventional drilling techniques because conventional techniques significantly reduce permeability. In the absence of permeability, oil and gas deposits cannot be recovered. Horizontal drilling greatly facilitates recovery of hydrocarbons, but traditional horizontal drilling techniques decrease permeability. The combination of underbalanced drilling and horizontal drilling makes it possible to maximize the productivity of a low permeability reservoir by not decreasing its permeability during the drilling process.
The interest in recovering deposits from more difficult reservoirs has increased the need for better underbalanced drilling techniques. Some underbalanced drilling situations require the ability to seal off the downstream portion of the tubing using a flapper valve at various stages of the drilling process. These underbalanced drilling situations also require the capability to pass a drill bit through the flapper valve when the flapper valve is open. In addition, these underbalanced drilling situations require a way to open the flapper valve against some downstream pressure resisting its opening without damage to the flapper valve.
Prior art devices for control of fluid flow in a tubing, known as check valves, are adaptable for underbalanced drilling application. One type of check valve, commonly referred to as a “flapper” check valve (hereafter “flapper valve”), contains a valve element hinged to pivot in the desired direction of flow. Some flapper valves use two semi-circular gate elements that pivot from a support in the center of the valve. Because a two gate flapper valve cannot allow a drill bit to pass through the tubing, only single gate flapper valves are suitable for under-balanced drilling situations. Moreover, in order to facilitate the flow of fluids and the passage of a drill bit, these single gate flapper valves must have gates that conform to the shape of the tubing when in the open position. Therefore, as used herein, the term flapper valve shall mean a valve with a single gate that conforms to the shape of the tubing when in the open position.
Single gate flapper valves can close perpendicularly to the tubing, or they can close at an acute angle to the high pressure side. U.S. Pat. No. 4,407,325 (the '325 patent) and U.S. Pat. No. 6,328,109 (the '109 patent) disclose flapper valves that close at an approximate ninety degree angle to the tubing wall. The '325 patent and the '109 patent flapper valves achieve conformity to the shape of the tubing by pivoting into a recess in the tubing or tubing assembly in the open position so that passage through the tubing in unimpeded when the valve is in an open position.
U.S. Pat. No. 5,044,396 (the '396 patent) and U.S. Pat. No. 5,099,877 (the '877 patent) disclose flapper valves that conform to the shape of the tubing when open, and that form an acute angle to the high pressure side. Conformity to the shape of the tubing in the open position minimizes pressure drop and energy loss. Additionally, the flapper valves of the '396 patent and the '877 anchor against the opposite side of the tubing from the valve hinge, and when closed the valves form an obtuse angle on the low pressure side and an acute angle on the high pressure side. The acute angle provides increased strength to the valve. Once closed, the valves of the '396 patent and the '877 patent can be opened by exertion of a greater pressure on the acute angle side than on the obtuse angle side.
U.S. Pat. No. 6,848,509, “Pressure Equalizing Plunger Valve for Downhole Use,” discloses a “thru-the-flapper” self equalizing system, (the '509 patent). In the '509 patent, a sleeve, which can be a concentric casing, slides down to open a flapper valve. The sleeve depresses a plunger in the valve to open an equalizing path prior to the valve opening and the '509 patent addresses improvements to reduce wear on the equalizing plunger.
In “Underbalanced Drilling Deployment Valve Introduction & Development Overview,” Techcorp Industries Inc. and Alpine Oil Services, Inc. (hereafter Techcorp) disclose a flapper valve with a sliding lower actuator extension mounted for sliding movement within the housing that opens the valve once the valve is equalized by the pumping of fluids through the valve in the closed position. The flapper is sealed within a flapper cage flush with the housing when the deployment valve is open. A flapper spring maintains the flapper in its closed position creating a seal between the flapper and the flapper seat. The deployment valve provides a through bore to allow passage of a drill bit. But when the flapper is subjected to downstream pressure, pressures must be equalized before the flapper can be opened. The lower actuator extension contacts the flapper at two points in the middle of the flapper, creating significant opening force on the valve hinge. Furthermore, the flapper closes at 90° with respect to the longitudinal axis of the housing, making it more difficult open. The Techcorp device is discussed in greater detail in FIG. 1 and FIG. 2 below.
FIG. 1 depicts prior art deployment valve 100 in its closed position. Deployment valve 100 is rendered hollow by through bore 110 through housing 124. Lower actuator extension 114, which is hollow, is slidably inserted into one end of deployment valve 100, and tubing 118 is threadedly attached by its male threads 120 to female threads 122 in the opposing end of deployment valve 100. Valve seat 108 encircles lower actuator extension 114 and has essentially the same inner diameter as the outer diameter of lower actuator extension 114. In its closed position, flapper 102 is urged by flapper spring 106 against valve seat 108 to prevent fluid within through bore 110 below flapper 102 from entering through bore 110 above flapper 102. Flapper pin 104 mounts flapper 102 within deployment valve 100. Flapper cage 112, in the form of a recess in housing 124, receives flapper 102 when deployment valve 100 is fully opened so that flapper 102 is flush within housing 124. Tubing 118 is a portion of a plurality of vertical tubing sections that have been connected together to make a semi-rigid drill string.
FIG. 2 depicts prior art deployment valve 100 in its open position. To open deployment valve 100, lower actuator extension 114 strikes flapper 102 at two contact points 116 (only one of which is visible) once pressures are equalized on either side of flapper 102. Because contact points 116 are halfway down flapper 102 from flapper pin 104, significant opening force is exerted on flapper pin 104, which may lead to its failure. Furthermore, unless flapper 102 and lower actuator extension 114 are manufactured very precisely and kept clean, lower actuator extension 114 will strike one contact point 116 before striking the opposite contact point 116. This imparts a rocking motion to flapper 102 and flapper pin 104, which may lead to their failure.
When deployment valve 100 is in its open position, lower actuator extension 114 has displaced flapper 102 into flapper cage 112 so that flapper 102 is flush within housing 124 and valve seat 108. Lower actuator extension 114 has essentially the same outer diameter as the inner diameter of through bore 110 (see FIG. 1) and the inner diameter of the end of tubing 118. Once deployment valve 100 is open, fluid can pass through lower actuator extension 114 and enter through bore 110 above flapper 102. When lower actuator extension 114 is returned to the position illustrated in FIG. 1, flapper spring 106 urges flapper 102 out of flapper cage 112 by inducing flapper 102 to pivot about flapper pin 104. Flapper 102 pivots until it contacts valve seat 108, thereby forming a seal perpendicular to the longitudinal axis of deployment valve 100 and closing deployment valve 100.
The prior art discloses opening a flapper valve in underbalanced drilling operations by either having an actuator engage an equalizing plunger on the valve before engaging the flapper to open the valve, or by equalizing pressure on both sides of the flapper before engaging the flapper to open the valve. Once the pressure is equalized, either by activating an equalizing plunger, or by other operations to equalize the pressure, the valve generally opens easily. But a valve that could be opened against a pressure differential would be advantageous, even if the pressure were reduced significantly so that a pressure differential approximated about 500 pounds per square inch. In such a case, the manner in which the prior art actuators engage the flapper can cause stress to the flapper hinge that could result in failure of the flapper hinge.
What is needed beyond the prior art is a flapper valve having a flapper and an actuator that does not require an equalizing plunger, that does not require pressure to be completely equalized on both sides of the flapper before engaging the flapper with an actuator in order to open the flapper, and that can maintain a seal in a reduced pressure differential environment prior to opening.